Tire pressure monitoring device

ABSTRACT

A device for monitoring the tire pressure on the basis of the signals provided by the individual wheel speed sensors includes an electronic evaluating circuit which determines correction factors for the wheel speeds of the individual wheels. The values of the individual correction phases are determined and stored in a learning phase. The deviation of the correction factors from the learnt values is detected and analyzed in an identification phase, and possible loss of tire pressure is signaled. A switch is mounted on the wheel suspension of each vehicle wheel which resets the memories, upon rebound of the wheel until its end position, and re-starts the learning phase for the correction factors.

BACKGROUND OF THE INVENTION

The present invention relates to a system for monitoring the tirepressure in mounted vehicle tires by measuring, comparing and evaluatingthe rotating speeds of the individual wheels, including wheel speedsensors, and an electronic evaluating circuit which determinescorrection factors for the wheel speeds of the individual wheelsrepresentative of the deviation of the respective wheel speed from areference quantity, the evaluating circuit determining and storing thevalues of the individual correction factors in a learning phase, anddetermining and evaluating the deviation of the instantaneous correctionfactors in consideration of the respective driving situation in anidentification phase, and signaling loss of tire pressure as soon as thedeviation of the instantaneous values from the learnt values inconsideration of the driving situation exceeds a predetermined amount.

A circuit arrangement of this type is disclosed in German patentapplication No. 43 37 443. The values for the individual correctionfactors are determined in the learning period. A band width or tolerancewidth for the correction factors responsive to the respective drivingsituation is determined by correlations between the correction factorsfor typical driving situations. Loss of tire pressure is signaled assoon as it is identified in the identification period that the tolerancewidth is exceeded.

The loss of tire pressure is identified during driving with the priorart device. The operation of the device is based on the knowledge thatthe air pressure in the tires influences the tire tread circumference.The dependence on pressure is, however, very insignificant and,therefore, difficult to measure. The wheel speed sensors which arealready required in a vehicle (for an anti-lock control system, forexample) can now be used to conclude a loss of pressure from the travelmeasurement and the comparison of the travels covered by the fourwheels. Because the changes in circumference of the tires can hardly beresolved, not even in the event of a major pressure loss, the sources ofdisturbances, more particularly, the different tire diameters due totire tolerances, tire mixing, different wear, or as a consequence ofassembly of an emergency wheel, must be eliminated in the signalanalysis. In the prior art tire pressure monitoring device, this iseffected by a calibration tip switch which the driver or the workshoppersonnel is required to operate manually, at least after each tirechange. The pressure monitoring system described will subsequently beadjusted in the learning phase to the existing differences in the tiretread circumferences of the individual wheels in response to thedistance covered and in consideration of the respective drivingsituation.

Experience has shown that drivers cannot be expected in each case toreliably operate the calibration tip switch. Therefore, an object of thepresent invention is to relieve the driver of the obligation of reliablyoperating the calibration tip switch and to find a most easy way, withleast possible effort, to start the learning phase in the necessaryintervals or after the occurrence of defined events.

SUMMARY OF THE INVENTION

It has been found that this object can be achieved by a system includingthat a sensor or switch is provided on the wheel suspension of eachvehicle wheel which, upon rebound of the wheel until its final positionor beyond a predetermined position, automatically triggers the resettingof the memories, which store the data acquired in the learning phase,and re-start of the learning phase. When required, an additional switchfor manually triggering the learning phase can be installed.

Limit switches or travel sensors are already mounted in the springstruts in some automotive vehicle control systems, for example, insuspension control systems. The switches or sensors can also be used ascomponent parts of the device of the present invention. In this case,no, or at least minimum, additional effort is needed in comparison tothe state of the art tire pressure monitoring device describedhereinabove, and the wanted relief of the driver of operating thecalibration tip switch is achieved nevertheless.

If the switches or sensors accommodated in the wheel suspension in thedevice of the present invention are operated during other maintenancework caused by lifting of the vehicle, this is no disadvantage butenhances the reliability in operation of the tire pressure monitoringdevice.

Further details of the present invention can be seen in the followingdescription of an embodiment of the present invention making referenceto the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing,

FIG. 1 is a schematically simplified view of the essential componentparts of a tire pressure monitoring device according to the presentinvention.

FIG. 2 is a schematic view of a vibration damper including a switch forthe device shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an automotive vehicle having wheels VL, VR, HL, HR whicheach include a rotational speed sensor S1, S2, S3, and S4. The sensorsare active or passive sensors which are stationarily mounted on thevehicle wheel and send an alternating signal reflecting the wheelrotational speed as soon as the wheel rotates and a toothed disc or anencoder E co-rotating with the wheels. Sensors of this type are known inthe art in a great number of design variations. Automotive vehiclesincluding an anti-lock system (ABS), a traction slip control system(TCS) or a driving stability control system (DSC, ASMS) require sensorsof this type to produce input quantities for the control.

The output signals of the sensors S1 to S4 are sent to a tire pressuremonitoring circuit 1, which comprises the electronic part of the deviceof the present invention, and processed in this circuit. Circuit 1 cancomprise hard-wired circuits and/or programmed circuits. The tirepressure monitoring circuit 1 can also be a component part of thecontroller of an automotive vehicle control system.

A sensor or switch T1 to T4, which closes or issues a signal as soon asthe wheel rebounds until a predetermined position or until the finalposition, is incorporated in the wheel suspension of each vehicle wheel,i.e., the front wheels VL, VR, and the rear wheels HL, HR. The outputsignals of the switches T1 to T4 are also sent to the monitoring circuit1.

The evaluating circuit of the device of FIG. 1, i.e., the tire pressuremonitoring device 1, processes, compares and analyzes in a known fashion(for example, according to the method disclosed in the above-mentionedGerman patent application No. 43 37 443) the signals provided by therotational speed sensors S1 to S4. Correction factors are produced foreach individual wheel, the values of which are calculated in a learningphase step by step in dependence on the driving distance covered. Therespective driving situation is found out and taken into considerationin the calculation steps. For example, a direct comparison of the wheelspeeds is only possible during straight travel. During cornering, thespeeds of the wheels of one axle are naturally different from eachother.

The circuit 1 is informed of the steering angle by way of an input LW.Another arrow BLS (brake light switch) and a dotted arrow indicate thatthe controller suitably includes further sensor signals and analyzesthem to judge the respective driving situation.

In an identification phase, the circuit 1 compares the learnt values orcorrection factors with the actual values and actuates a warning lamp WLas soon as a loss of tire pressure is recognized in the analysis of thepresent values of the wheel speed sensors S1 to S4.

FIG. 2 shows an embodiment relating to the installation of a positionswitch T1′ which is accommodated in a vibration damper 2 of the frontwheel VL. Upon rebound of the front wheel, as soon as a representedpiston 3 in the interior of the vibration damper 2 reaches its top endposition, the switch T1′ will be actuated mechanically or magneticallyso that it signals the rebound of the wheel to the evaluating circuit 1.The signal of one of the limit switches or position switches T1 to T4 isalready sufficient to re-start the learning phase of the evaluatingcircuit 1 of the device of the present invention, and to calibrate thesystem thereby. Action of the driver or the maintenance staff is notrequired.

Instead of the position switch T1 to T4, any other switch or sensorwhich is already provided in the vehicle can be used to indicate therebound of the vehicle wheel (for example, the switch/sensor used forthe suspension control).

An additional manual switch HS is provided in exceptions only.

The switches T1 to T4 are automatically operated whenever the vehicle islifted by way of a vehicle hoist and during each wheel change, as thewheel first hangs while the vehicle is suspended, and then rebounds to anormal operating position when the vehicle is returned to the ground.Inadvertent rebound of the wheel in an exceptional situation and arelated actuation of one of the switches T1 to T4 is harmless withrespect to functioning of the tire pressure monitoring device.

What is claimed is:
 1. A system for monitoring the tire pressure inwheels mounted on an automotive vehicle by measuring, comparing andevaluating the rotating speeds of individual wheels, the systemincluding wheel speed sensors and an electronic evaluating circuit,wherein the circuit is adapted to determine correction factors for therotating speeds of the individual wheels representative of a deviationof the respective rotating speeds from a reference quantity, and isfurther adapted to store the reference quantity during a learning phase,and to determine and evaluate deviations of the correction factors fromthe reference quantity during an identification phase in considerationof a prevailing driving situation, and is further adapted to signal aloss of tire pressure as soon as the deviations exceed a predeterminedamount; the improvement comprising: a wheel suspension with a signalingelement, provided for each wheel, the element being adapted to send asignal to the circuit to automatically trigger a resetting of memories,which comprise data acquired and stored in the learning phase, and are-start of the learning phase of the evaluating circuit upon rebound ofthe wheel to a predetermined extent.
 2. The system of claim 1, furthercomprising a switch for manually resetting the memories and re-startingthe learning phase.
 3. The system of claim 1, wherein the element is asensor.
 4. The system of claim 3, further comprising a switch formanually resetting the memories and re-starting the learning phase. 5.The system of claim 1, wherein the element is a switch.
 6. The system ofclaim 5, further comprising a second switch for manually resetting thememories and re-starting the learning phase.